1. Field of Invention
The present invention pertains to pilot valves used in downhole completions, and particularly to a pilot valve using an actuator to control the state of the pilot valve, and thereby the state of the main valve.
2. Related Art
Pilot valves are used in gas lift product lines such as intermittent gas lift applications. Existing pilot valves are typically driven by a bellows operating in response to a pressure differential, similar to what is used in other types of gas lift valves. Although the present invention can be used for intermittent gas lift, it is not limited to that application.
Actuator valves such as solenoid valves, for example, are used in various industrial and downhole applications. Because of the linear relationship between the port size and solenoid force requirement, pilot valves have been used in many solenoid-actuated valves to maximize pressure ratings. In many existing downhole tool designs, two bellows are used to seal and isolate reservoir fluids from the fluid in the interior of the solenoid. In addition, the two-bellows configuration allows the pressure to balance between those fluids. The most intuitive way of configuring two bellows is to have two separate bellows; one for sealing and the other for pressure balancing. However, because of space constraints, it may be more advantageous to achieve both functions using only one fluid contact surface. In U.S. Pat. No. 2,880,620, Bredtschneider describes a system having two telescoping bellows for this purpose. In U.S. Pat. No. 5,662,335, Larsen describes a system that achieves the same purpose by assembling two bellows in an end-to-end arrangement.